The following subject matter relates to inkjet imaging mechanisms. More particularly, the subject matter pertains to an inkjet printhead cleaner service station system architecture for servicing staggered printheads.
Printers are imaging devices that print characters onto a printing medium such as a sheet of paper or a polyester film. Printers of many types are available that are controlled by a computer that supplies the images in the form of text or figures that are to be printed. Some printers use a colorant-containing liquid, which may be a dye or ink, to form the images on the printing medium. (By contrast, other imaging devices use a dry toner to form the image). Such printers deliver the colorant to the medium using a printhead that creates the proper patterning of colorant permanently recording the image on the print medium.
One type of imaging device is the thermal inkjet printer, which forms small droplets of ink that are subsequently ejected toward the printing medium in a pattern of dots or pixels that form the images. An ink jet printer typically has a large number of individual colorant-ejection nozzles in a printhead. A carriage supports a printhead that is oriented in a facing, but spaced-apart, relationship to the printing medium. The carriage and supported printhead traverse over the surface of the medium with the nozzles ejecting droplets of colorant at appropriate times under command of the computer or other controller to produce a swath of ink droplets.
The colorant droplets strike the medium and then dry to form dots that when viewed together form one swath or row of the printed image. The carriage is moved an increment in the direction lateral to traverse (or, alternatively, the printing medium is advanced), and the carriage again traverses the page with the printhead operating to deposit another swath. In this manner, the printhead progressively deposits the entire pattern of dots that form the image is by during a number of traverses of the page. To achieve the maximum output rate, the printing is preferably bi-directional, with the printhead ejecting colorant during traverses from left-to-right and right-to-left.
Color inkjet printers utilize several, typically four, different printheads mounted in the print carriage to produce both primary and secondary colors. Each of the printheads produces a different color, with four often-used colors being cyan, yellow, black, and magenta. These primary colors are produced by depositing a droplet of the required color onto a dot location. Depositing multiple droplets forms secondary or shaded colors of different color inks onto the same pixel location, with the overprinting of two or more primary colors producing secondary colors according to well-established optical principles.
Good print quality is one of the most important considerations and basis of competition in the inkjet printer industry. Since images are formed of thousands of individual dots, the quality of the image is ultimately dependent upon the quality of each dot and the arrangement of the dots on the print medium. Because of the fashion in which printing occurs, the quality of the dots can have a surprisingly large effect upon the final image quality.
To illustrate this, consider that when ink blobs or particulate plug inkjet printhead nozzles, color image quality can be negatively affected, or otherwise contaminated with internal bubbles that prevent the nozzles from operating properly. To maintain image quality in view of such ink nozzle plugging, inkjet printers typically include a service station with one or more printhead cleaners to protect and clean printhead ink nozzles.
During operation, clogs in a printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as xe2x80x9cspitting,xe2x80x9d with the waste ink being collected in a spittoon reservoir portion of the printhead cleaner. For storage, or during non-printing periods, the cleaner includes a capping system to hermetically seal printhead nozzles from contaminants and drying. Occasionally during printing, an elastomeric wiper wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the face of the printhead.
In yet another example, color image quality can be negatively affected during the bi-directional printing of secondary colors, wherein overprinting of two primary colors produces each dot. In particular there can be perceived color shift due to the different appearance of a droplet of a first color deposited over a droplet of the second color, as compared with a droplet of the second color deposited over a droplet of the first color. In other words, printed color depends on the order in which various color inks are placed on print media by an imaging device.
To illustrate such undesired color shifting, consider FIGS. 1 and 2, which show a number of printheads 114 laying down color in respective directions onto print media 110. Referring to FIG. 1, consider that an imaging device (not shown) uses four printheads to image color. Each printhead is configured to image one of cyan (C), yellow (Y), magenta (M), and black (K) inks. Specifically, printhead 114-1 images C, printhead 114-2 images Y, printhead 114-3 images M, and printhead 114-4 images K.
These printheads 114 are attached to a carriage (not shown) and aligned with respect to one another relative to a print-media-advance axis. The imaging device prints bi-directionally, meaning that the device prints respective color swaths as the printheads are moved from left-to-right and from right-to-left with respect to print media 110. Arrow 112 illustrates the direction of printhead movement. When the printheads are moved from left-to-right, a first sequence CYMK of color ink is imaged upon the print media. In other words, C is overprinted by Y, Y is overprinted by M, and M is overprinted by K.
Referring to FIG. 2, as the imaging device moves the same four printheads 114 from right-to-left a second sequence KMYC of color inks is imaged upon the print media. (Arrow 202 illustrates the direction of printhead movement). In other words, K is overprinted by M, M is overprinted by Y, and Y is overprinted by C. This second sequence KMYC is exactly opposite the first sequence CYMK that was laid down on the print media when the printheads were moving from left-to-right.
Bi-directional hue shift typically results when inks are imaged on print media is different orders from swath-to-swath. Specifically, bi-directional hue shifts are perceived color changes determined both by how the various color layers mix when overprinted on another color and by how the various mixes react with light. Such defects are especially prevalent on imaging devices that print in xe2x80x9c1-pass bi-directionalxe2x80x9d modes, meaning that a printhead prints only a single time in the same area of print medium.
FIG. 3 shows an example of a conventional technique used by imaging device manufacturers to address undesired bi-directional hue shift imaging defects. Specifically, a staggered printhead configuration 300 is used to address such imaging defects. In this configuration, a cyan (C) printhead 302-1, a magenta (M) printhead 302-2, and a yellow (Y) printhead 303-3 are staggered such that no printhead 302 is on the same horizontal plane as any other printhead 302. This particular configuration 300 of the printheads 302 forces all ink drops or colors (C, M, and Y) to be imaged on a print medium (e.g., paper) in the same order, regardless of whether the printheads are imaging from left-to-right or from right to left with respect to print medium. Optionally, this conventional staggered configuration may include a black ink imaging printhead, which is not shown.
Existing color inkjet printers produce images of acceptable quality and are widely used. However, there is a continuing need for improved inkjet printers and imaging procedures to print high-quality images. Unfortunately, conventional inkjet imaging device designs and procedures have some significant limitations when addressing printhead nozzle ink clogging issues when the printheads are in a staggered configuration (e.g., as illustrated in FIG. 3).
Methods and arrangements are provided to service multiple staggered printheads in a color inkjet-imaging device. Multiple cleaning units are attached to a service station. Each cleaning unit includes multiple components to service a particular one printhead. Each cleaning unit is offset from an adjacent cleaning unit to form a staggered configuration to service the staggered printheads. The staggered printheads are moved from/to the service station to/from a print zone. The staggered cleaning unit configuration in combination with component positioning provides substantially unhindered access to move the staggered printheads into and out of the service station. Responsive to moving the staggered printheads into the service station, the cleaning units service the staggered printheads